Similarities and differences in microwave and optical radiation detection

The differences and similarities between the detection processes involved in the microwave and visible electromagnetic (EM) waves are presented for the case of two beam superposition. A microwave receiver measures the motion of conduction electrons which responds linearly to the superposed time dependent EM field amplitudes. A visible light detector also responds to the superposition of the EM field amplitudes due to interactions with the detecting dipoles. However, the visible light detector measures the quantum of energy absorbed and responds to the square modulus of the superposition of the time dependent amplitudes of the EM fields. The measured current in the microwave detector is directly proportional to the superposed microwave amplitudes. The measured energy in visible light detector is directly proportional to the square modulus of the superposed visible light amplitudes. We will highlight the similarities and differences in the detection processes. These important similarities and difference are not underscored in most optics textbooks.